1. Field of the Invention
The invention relates to a semiconductor light-emitting device, and more particularly, to one with II-V group (or II-IV-V group) compound contact layer. With respect to the technology background of the invention, please refer to the following references:    [1] K. Kuriyama, Yukimi Takahashi, F. Sunohara. Optical band gap of Zn3N2 films. PHYSICAL REVIEW B 1993;48(4):2781-2782;    [2] B. Chelluri, T. Y. Chang, A. Ourmazd, A. H. Dayem, J. L. Zyskind, A. Srivastava. Molecular beam epitaxial growth of the II-V semiconductor compound Zn3As2. Appl. Phys. Lett. 1986;49(24):1665-1667;    [3] M. Sieberer, J. Redinger, S. Khmelevskyi, P. Mohn. Ferromagnetism in tetrahedrally coordinated compounds of I/II-V elements: Ab initio calculations. PHYSICAL REVIEW B 2006,73(024404):1-9; and    [4] C M Fang, R A de Groot, R J Bruls, H T Hintzen, G de With. Ab initio band structure calculations of Mg3N2 and MgSiN2. J. Phys. 1999;Condens. Matter 11:4833-4842.
2. Description of the Prior Art
Light-emitting diodes can be applied to various kinds of equipments, such as optical display equipments, regulatory signs, telecommunication equipments, and illuminating equipments. Light-emitting diodes, distinct from the conventional light sources, are applicable to different industries.
Compared to the tungsten lamps of prior art, light-emitting diodes consume less electricity and respond more quickly. Furthermore, light-emitting diodes have better illuminating efficiency, longer life time, and smaller size; they also consume less power and do not have hazardous substances like mercury.
The radiating principle of the light-emitting diodes is that the bonding of electrons and holes in the light-emitting layer of P-type and N-type semiconductors forms photons to generate light on forward bias. Because the P-type GaN semiconductor is hard to be doped, the contact of P-type GaN semiconductor and conductive layer produces higher resistance and consequently decreases the efficiency of P-type GaN semiconductor.
Taiwanese Patent No. 459,407 provides a proposal to reduce the contact resistance between a P-type GaN semiconductor layer and a conductive layer. Referring to FIG. 1, FIG. 1 illustrates a light-emitting diode structure having an n+ type reverse tunneling layer. The light-emitting diode structure includes an insulated sapphire substrate 11, a GaN buffer layer 12, an N-type GaN contact layer 13, an N-type AlGaN constraint layer 14, an InGaN light-emitting layer 15, a P-type AlGaN constraint layer 16, a P-type GaN contact layer 17, an n+ type reverse tunneling layer 18, a transparent conductive layer 19, a first electrode 21, and a second electrode 22.
The GaN buffer layer 12 is formed on the insulated sapphire substrate 11. An N-type GaN contact layer 13 is formed on the GaN buffer layer 12 such that a partial area of the N-type GaN contact layer 13 is exposed. The first electrode 21 is formed on the exposed partial area of the N-type GaN contact layer 13. The N-type AlGaN constraint layer 14 is formed on the N-type GaN contact layer 13. The InGaN light-emitting layer 15 is formed on the N-type AlGaN constraint layer 14. The P-type AlGaN constraint layer 16 is formed on the InGaN light-emitting layer 15. The P-type GaN contact layer 17 is formed on the P-type AlGaN constraint layer 16. The n+ type reverse tunneling layer 18 is formed on the P-type GaN contact layer 17. The transparent conductive layer 19 is formed on the n+ type reverse tunneling layer 18 such that a partial area of the n+type reverse tunneling layer 18 is exposed. The second electrode 22 is formed on the exposed partial area of the n+ type reverse tunneling layer 18 and contacts the transparent conductive layer 19.
The light-emitting diode improves the ohmic contact between the P-type GaN contact layer 17 and the transparent conductive layer 19 by adding an n+ type reverse tunneling layer 18 between them.
However, due to a complex manufacturing process and difficult control of the n+type reverse tunneling layer 18, the finished products of light-emitting diodes are not stable and have a higher production cost as well.
Accordingly, a scope of the invention is to provide a semiconductor light-emitting device with II-V group (or II-IV-V group) compound contact layer, capable of improving the ohmic contact between the P-type GaN contact layer and the transparent conductive layer. Moreover, the semiconductor light-emitting device with II-V group (or II-IV-V group) compound contact layer has an easier manufacturing process; it also increases the stability for production and consequently has a lower production cost.